The present invention relates to a balance with a weighing compartment, a balance housing, a carrier for the weighing load, and a calibration device with a receiving element for the calibration weights.
Balances of this type serve mainly as analytical balances and are used widely in laboratories.
A balance meeting the foregoing description is disclosed in U.S. Pat. No. 4,766,965. The weighing pan is supported by a cantilever arm that is attached to and projects forward from the bottom end of the load receiver of the weighing cell. The weighing pan is arranged immediately above the floor of the weighing compartment and is connected to the cantilever arm through an opening in the floor. A calibration device with a mechanism for raising and lowering the reference weights is arranged below the floor of the weighing compartment.
In U.S. Pat. No. 4,566,548, a balance is described with an L-shaped cantilever arm extending below the floor of the weighing compartment, where the balance pan is supported on the horizontal leg of the L. The support connection passes through an opening in the floor of the weighing compartment. The vertical leg of the L of the cantilever arm is attached by way of a U-shaped holder to the movable end of the parallelogram linkage of the weighing cell. Two cylindrical reference weights are arranged immediately below the floor of the weighing compartment and are secured in a fixed position by a weight-lifter mechanism. To calibrate the balance, one or the other or both of the weights are selectively lowered onto a weight-receiving element on the cantilever arm.
A further balance in the same general category is described in JP 62-266421, disclosing a concept where the weighing pan as well as a cantilever arm supporting the weighing pan are arranged above the floor of the weighing compartment. The support arm for the weighing pan is connected to the inner working mechanism of the balance through a passage opening in the rear wall of the weighing compartment.
All of the aforementioned known balances suffer from the drawback that they have relatively large passage openings through the floor or the rear wall of the weighing compartment, so that contaminants can easily get inside the balance housing.
It is therefore the object of the present invention to propose a balance that is or can be equipped with a user-operated calibration device, that has a compact design, is less susceptible to contamination, and can be used in a multitude of applications.
According to the invention, the foregoing objective is realized in a balance with a balance housing that contains a weighing cell and forms the rear wall and the floor of a weighing compartment. The balance has a weighing-load carrier held by a cantilever arm of the weighing cell. Connected to the cantilever arm are a receiving element for the weights of a calibration device and a coupling arrangement for the weighing-load carrier that projects through openings in the rear wall. The coupling arrangement is designed so that the weighing-load carrier can be taken off the balance. The floor of the weighing compartment completely separates the weighing-load carrier from the receiving element for the calibration weights.
The balance according to the invention is distinguished by its compact design. The inventive configuration represents, in effect, a dual-cantilever system with one cantilever arm supporting the receiving element for the calibration weights and the other cantilever arm being constituted by the weighing-load carrier. The openings required for the coupling arrangement of the weighing-load carrier are small in comparison to the passages performing an analogous function in state-of-the-art balances. A balance designed according to the present invention is therefore drastically less susceptible to dirt contamination. The inventive arrangement offers a multitude of application possibilities, as will be described below through examples, and it also optimizes the operation of the balance from an ergonomics point of view.
Preferably, the center of the weighing-load carrier is located vertically above the center of gravity of the calibration device.
The weighing-load carrier in a preferred embodiment of the invention is configured as a plane horizontal grate. This has many possible applications for weighing in a laboratory. For example, receptacles or devices of the most diverse kinds can be set on the grate and/or clamped to the grate. Spilled sample material does not stay on the weighing-load carrier but drops off between the bars of the grate, so that the spilled material cannot inadvertently be included in a weighing. In a particularly favorable design, the bars of the grate have a roof-like triangular profile with a ridge at the top, which ensures even better that spilled sample material will drop off the grate. Using a grate as weighing-load receiver has also particular advantages for fastening different kinds of holders for sample containers.
According to a further preferred embodiment of the invention, the weighing-load carrier itself is configured as a holder for one or more laboratory vessels. The holder may also be arranged so that it can be tilted at different angles.
To facilitate cleaning of the weighing compartment, it is advantageous to arrange a fixed or removable spill-collector plate on the floor of the weighing compartment to catch spilled weighing sample material.
In an advantageous further development of the invention, the inside rear wall of the weighing compartment is equipped with a holder system for accessory devices that can be used inside the weighing compartment. This provides the flexibility of using the balance for different kinds of applications and/or experiments that can be performed inside the weighing compartment.
In a preferred embodiment of the invention, the holder system is configured as a portion of the rear wall that projects into the weighing compartment like a column and has grooves in the laterally facing flanks. The openings for the coupling arrangement of the weighing-load carrier can be to the sides of the holder arrangement or they can be in the flanks of the column, aligned with the grooves.
A preferred embodiment of the invention has a load-relief mechanism to lift the load off the weighing-load carrier. The load-relief mechanism is arranged at the rear wall and has a lift platform shaped like a grid of bars or spaced-apart lamellae. When the lift platform is raised, the bars or lamellae of the lift platform come up through the gaps between the bars of the weighing-load carrier and lift the weighing object off the carrier grate. With the load-relief mechanism, it is not necessary to remove and subsequently return the weighing load when re-zeroing the balance. Thus, a potential source of weighing errors is avoided. It is also possible to perform long-term weight studies and recalibrate the balance between the individual weighings.
To facilitate cleaning of the balance, the lift platform is designed to be easily disassembled. Preferably, the load-relief mechanism is motorized.
Other advantageous embodiments of the balance according to the invention provide the possibility of integrating code-identification systems or set-ups for experiments into the balance, e.g., for turbidity measurements, to make certain work processes more efficient.
Advantageous traits of a balance according to the invention are its compact design and its modular configuration that make it remarkably versatile for a variety of laboratory applications. The inventive balance is distinguished by its flexibility and by how quickly it can be reconfigured for different applications. In addition, cleaning the separate components is very easy.